Integrated circuit processing system

ABSTRACT

A vacuum-tight wafer carrier, and a load lock suitable for use with this wafer carrier. The wafers are supported at each side by a slightly sloping shelf, so that minimal contact (line contact) is made between the wafer surface and the surface of the shelf. This reduces generation of particulates by abrasion of the surface of the wafer. The carrier also contains elastic elements to restrain the wafers from rattling around, which further reduces the internal generation of particulates. When the wafer carrier is placed into the load lock, its body is lowered from beneath its cover through an aperture into a lower chamber, where wafers are loaded and unloaded under vacuum; the carrier cover remains covering the aperture into the lower chamber, so that the wafers never see any surface which is directly exposed to atmosphere. A wafer transport arm mechanism permits interchange of wafers among one or more processing stations and one or more load locks of this type.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of contract No.N00014-85-C-0286 awarded by DARPA.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 114,812, filed Oct. 29, 1987now U.S. Pat. No. 4,966,519 which is a division of Ser. No. 061,017filed on June 12, 1987, now abandoned, which is a continuation of Ser.No. 824,342 filed on Jan. 30, 1986 now abandoned which is acontinuation-in-part of Ser. No. 790,708 filed Oct. 24, 1985, nowabandoned Ser. No. 790,918 filed Oct. 24, 1985, now abandoned and Ser.No. 790,924 filed Oct. 24, 1985, now U.S. Pat. No. 4,687,542.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to apparatus for manufacturing ofintegrated circuits.

One of the basic problems in integrated circuit manufacturing isparticulates. This problem is becoming more and more difficult, becauseof two trends in integrated circuit processing: First, as devicedimensions become smaller and smaller, it is necessary to avoid thepresence of smaller and smaller particles. This makes the job of makingsure that a clean room is really clean increasingly difficult. Forexample, a clean room which is of class 1 (has one particle per cubicfoot) for particles of one micron and larger may well be class 1000 orworse if particle sizes down to 100 angstroms are counted.

Second, there is increased desire to use large size integrated circuitpatterns: for example, integrated circuit sizes larger than 50,000square mils are much more commonly used now than they were five yearsago.

Thus, particulates are not only an extremely important source of loss inintegrated circuit manufacturing, but their importance will increasevery rapidly in the coming years. Thus, it is an object of the presentinvention to provide generally applicable methods for fabricatingintegrated circuits which reduce the sensitivity of the process toparticulate contamination.

One of the major sources of particulate contamination ishuman-generated, including both the particles which are released byhuman bodies and the particles which are stirred up by equipmentoperators moving around inside a semiconductor processing facility(front end). To reduce this, a general trend in the industry for severalyears has been to make more use of automatic transfer operations,wherein a technician can, for example, place a cassette of wafers into amachine, and then the machine automatically transfers the wafers, one byone, from the cassette through the machine (to effect the processingsteps necessary) and back to the cassette, without the technician'shaving to touch the wafers.

However, the efforts in this direction have served to highlight theimportance of a second crucial source of particulates, which isparticulates generated internally by the wafers and/or transfermechanism. That is, when the surface of the wafer jostles slightlyagainst any other hard surface, some particulates (of silicon, silicondioxide, or other materials) are likely to be released. The density ofparticulates inside a conventional wafer carrier is typically quitehigh, due to this source of particulates. Moreover, many of the priorart mechanisms for wafer transport will themselves generate substantialquantities of particulates.

The present invention advantageously solves this problem, by providing awafer carrier wherein particulate generation during transport is reducedin several ways. First, the door of the vacuum carrier contains elasticelements to press the wafers lightly against the back of the carrierbox. Thus, when the door of the box is closed, the wafers are restrainedfrom rattling around, which reduces the internal generation ofparticulates. Second, the wafers are supported at each side by aslightly sloping shelf, so that minimal contact (line contact) is madebetween the wafer surface and the surface of the shelf. This reducesgeneration of particulates by abrasion of the surface of the wafer.

The present invention not only reduces generation of particulates in thecarrier during transport and storage, but also advantageously reducestransport of particulates to the wafer face during transport andstorage, by carrying the wafers face down, under a high vacuum. Theprior art is not know to address this problem at all.

This wafer carrier design permits use with a wafer transport mechanismaccording to the present invention (and also disclosed in parentapplications as filed) to provide a complete low-particulate wafertransport system.

The current state of the art wafer loading mechanisms used in thesemiconductor industry consist primarily of three basic types: beltdriven wafer transport, air track driven wafer transport, and arm drivenwafer transport (using either vacuum coupling or nesting to hold thebottom or the edge of the wafer). However, all of these types of systemstypically use face up wafer movement into and out of the carrier,vertical movement of the wafer carrier during the loading and unloadingoperations, wafer transfer under pressures ranging from atmospheric tolow vacuum, and a requirement that wafers be unloaded in the reverseorder of loading. The prior art methods accordingly have a number ofimportant disadvantages, as follows:

First, wafers which are transported face up are more likely to catchparticles generated by particle generation mechanisms inside the wafercarrier or inside the wafer loader unit.

Second, vertical movement of the wafer carrier during the loading andunloading operation creates many particles, due to rattling of thewafers in the carrier. These particles can fall directly onto the activeface of adjacent wafers resting face up in the carrier.

Third, belt mechanisms will typically scrub the bottom of the waferduring loading and unloading operations, again creating manyparticulates due to abrasion.

Fourth, air track transport will stir many particulates around by aircurrents, and many of these particulates can come to rest on the activeface of the wafer.

Fifth, the drive mechanisms of many loader modules are housed within thesame area as the open wafer carrier will be, in close proximity to thewafers being processed. This has great potential for gross amounts ofcontamination.

Sixth, the mass of the carrier wafer combination changes as the wafersare loaded and unloaded, and this can affect the reliability andpositioning of the wafer carrier vertical drive, particularly wherelarge wafers (such as 150 millimeters or larger) are being handled.

Seventh, two loading modules are typically used for each processingstation, so that one cassette is typically progressively loaded, and thewafers from this cassette which have been processed are loaded into asecond cassette.

Eighth, loss of equipment utilization efficiency occurs every time a newcassette of wafers is loaded into or out of each processing station,since the machine must be idled while the cassette is removed.

The present invention provides advantageous solutions to all of theabove problems, and achieves greatly improved low particulate waferhandling and loading operations.

One key advantage of the present invention is that wafers can betransported, loaded and unloaded without ever seeing atmospheric or evenlow vacuum conditions. This is extremely useful, because, at pressuresof less than about 10⁻⁵ Torr, there will not be enough Brownian motionto support particulates of sizes larger than about 10 nm, and theseparticulates will fall out of this low-pressure atmosphere relativelyrapidly.

FIG. 2 shows the time required for particles of different sizes to fallone meter under atmospheric pressure. Note that, at a pressure of 10⁻⁵Torr or less, even 10 nm particles will fall one meter per second, andlarger particles will fall faster. (Large particles will simply fallballistically, at the acceleration of gravity.) Thus, an atmosphere witha pressure below 10⁻⁵ Torr means that particles ten nanometers or largercan only be transported ballistically, and are not likely to betransported onto the critical wafer surface by random air currents orBrownian drift.

The relevance of this curve to the present invention is that the presentinvention is the first to provide a way to transport wafers from oneprocessing station to another, including loading and unloading steps,without ever exposing them to higher pressures than 10⁻⁵ Torr. Thismeans that the wafers are NEVER exposed to airborne particulates, fromthe time they are loaded into the first vacuum processing station (whichmight well be a scrubbing and pumpdown station) until the time whenprocessing has been completed, except where the processing step itselfrequires higher pressures (e.g. in conventional photolithographystations or for wet procesing steps). This means that the totalpossibilities for particulate collection on the wafers are vastlyreduced.

A key element of this advantage is that the present invention provides amethod and apparatus for loading and unloading a vacuum carrier underhard vacuum.

The present invention provides a load lock which includes an apparatusfor opening a vacuum wafer carrier under vacuum, for removing wafersfrom the carrier in whatever random-access order is desired, and forpassing the wafers one by one through a port into an adjacent processingchamber, such as a plasma etch chamber. Moreover, the load lock of thepresent invention is able to close and reseal the wafer carrier, so thatthe load lock itself can be brought up to atmospheric pressure and thewafer carrier removed, without ever breaking the vacuum in the wafercarrier.

A particular advantage of the preferred embodiments of the presentinvention is that the mechanical apparatus preferably used for wafertransfer is extremely compact. That is, by providing a transfer armpivoted on an arm support, with gearing or a chain drive inside the armsupport so that the rotation of the arm support causes twice as muchrotation of the transfer arm with respect to the arm support, a compactapparatus is provided which can rest in the home position and require nomore clearance than the length of the arm support in one direction, butcan be extended, by a simple rotary shaft motion, out to the length ofthe arm support plus the length of the transfer arm in either of twodirections.

A further advantage of the preferred embodiments of the presentinvention is that the motors used to extend the transfer arm and tochange its elevation are both held inside an exhaust manifold, so thatparticles generated by these moving mechanical elements do not tend toreach the interior of the load lock chamber where wafers are exposed.

A further advantage of the invention is that a transfer arm is providedwhich can handle wafers face down with minimal damage to device areascaused by contact with the transfer arm.

A further advantage of the present invention is that the presentinvention provides a wafer transfer apparatus which can handle waferswith minimum generation of particulates caused by the handlingoperation.

A further advantage of the present invention is that the presentinvention provides a transfer apparatus which can handle wafers withessentially no generation of particulates due to abrasion, sinceessentially no sliding contacts are made.

Another advantage of the wafer transport mechanism of the presentinvention is that control is simplified. That is, the transfer armpreferably used has only two degrees of freedom, and positionregistration is provided so that the transfer arm control can beprovided very simply (by use of stepper motors or comparable apparatus),without the need for sensors to detect the position of or forces on thearm.

A related advantage of the wafer transport mechanism of the presentinvention is that it is a stable mechanical system. That is, smallerrors in positioning do not accumulate, but are damped out by inherentnegative feedback provided by some of the mechanical elements used. Thisalso facilitates the advantage of simple control.

A further advantage of the present invention is that the wafer handlingequipment used in the load lock takes up minimum volume. Since the loadlock is of such small volume, vacuum cycling can be performed rapidlywithout requiring very expensive large vacuum pumps.

An even more important consequence of the volume efficiency of wafertransport according to the present invention is that the upper portionof the load lock (wherein the defect-sensitive surfaces of wafers beingtransferred will be exposed) will therefore have a small surface area.It is desirable to have as little surface area as possible withinline-of-sight of the wafer surface, and it is also desirable to have aslittle surface area as possible in close proximity to the wafer surface,whether it is within line-of-sight or not. All surface area in the upperpart of the load lock (i.e. the part above the exhaust manifold)presents two hazards: first, all surface area will desorb gasses, sothat the more surface area is in the upper chamber the more difficult itwill be to pull a hard vacuum. Second and more important, all surfacearea has the potential to hold adherent particulates, which can later beexpelled by mechanical vibration or shock to fly ballistically onto thewafer surface, even under high vacuum. Thus, the volumetric efficiencyof the load lock according to the present invention means that thepotential for ballistic transport of particulates onto the wafer surfaceis reduced.

Moreover, the alternative embodiment disclosed in thiscontinuation-in-part application has the further advantage that thewafers themselves do not ever see even the surfaces in the load lockwhich were exposed to particulates during loading of the carrier intothe lock. In this embodiment the wafer carrier has a vacuum-sealablevertically removable cover, instead of a vacuum sealable hinged door,and, after the carrier is positioned in an upper chamber (the primaryload lock) the carrier body is lowered from beneath the cover into alower chamber while the cover remains in place and covers the aperturebetween upper and lower chambers. Thus, the wafer carrier body, and thewafers in it, not only never see dirty ambient atmosphere, they nevereven see surfaces which are exposed to dirty ambient atmosphere.

Another advantage resulting from the compactness of the wafer handlingequipment in a load lock according to the present invention is thatclean room floor space (which is very expensive) is not excessivelyconsumed by such an apparatus.

Another advantage of the wafer carrier described in the present patentapplication is that this wafer carrier cannot inadvertently be openedoutside a clean room. A substantial yield problem in conventional cleanroom processing is inadvertent or careless exposure of wafers toparticulates by opening the wafer carrier outside the clean roomenvironment. However, with the wafer carrier of the present inventionthis is inherently impossible, since the pressure differential on thedoor of the carrier holds it firmly shut except when the carrier is invacuum. This is another reason why the present invention is advantageousin permitting easy transport and storage of wafers outside a clean roomenvironment.

In a further class of embodiments of the present invention, a processmodule (which may optionally contain one process station or more thanone process station) has more than one load lock according to thepresent invention attached to it. Thus, processing can continue onwafers transferred in from one load lock while the other load lock isbeing reloaded. Moreover, the provision of two transfer mechanisms meansthat, if a mechanical problem occurs with one transfer apparatus insideits load lock, the processing station can continue in production, usingtransfer through the other load lock, while a technician is summoned tocorrect the mechanical malfunction. Thus, this class of embodiments hasthe advantage of greater throughput. The load lock may be connected to avacuum pump capable of pulling a vacuum higher than 10 to the -3 Torr.

According to the present invention there is provided: a method forfabricating integrated circuits, comprising the steps of: providing aplurality of wafers in a vacuum sealable wafer carrier box, said wafercarrier box comprising a cover which is vacuum sealed to a body thereof,said cover being removable from said body in a direction which issubstantially normal to the plane of wafers supported in said body;placing said wafer carrier box into a vacuum sealable load lock upperchamber having a partial floor with an aperture therein and a stagepositioned below said aperture in close proximity to said floor; pumpingdown said load lock upper chamber to a pressure less than 10⁻⁴ Torr;lowering said stage, so that said cover remains supported on saidpartial floor in said upper process chamber while said body includingwafers is lowered into the lower chamber; transferring wafers in adesired sequence from said wafer carrier under vacuum to one or moreselected process stations which are enclosed inside a connectingcontiguous vacuum-tight space with said lower chamber until a desiredsequence of processing operations has been completed; and then raisingsaid stage to rejoin said wafer carrier body with said wafer carriercover and again effect a vacuum seal therebetween; venting said upperchamber to ambient; and removing said wafer carrier from said upperchamber.

According to the present invention there is provided: a wafer carriercomprising: a wafer carrier body including supports which include ledgestapered to support a flat disk with substantially line contact and notarea contact; said wafer carrier having said supports continuous with abase, said base including a vacuum seal thereon surrounding said sidesupports; said wafer carrier further comprising a cover, said coverbeing shaped to mate with said vacuum seal of said wafer carrier body,said cover, said vacuum seal, and said body defining a vacuum tightenclosure, said cover being removable from said body in a directionsubstantially normal to the plane of said vacuum seal.

According to the present invention there is provided: a wafer carriercomprising a body including sidewalls and also a cover closeable to makea vacuum-tight seal with said body, said sidewalls each having pluralledges thereon defining slots to hold wafers of a predetermined size,said ledges on said sidewalls having at least one surface thereof slopedto be at least 5 degrees out of parallel with the plane of said slots.

According to the present invention there is provided: a wafer carriercomprising a body including sidewalls and also a cover closeable to makea vacuum-tight seal with said body, said sidewalls each having pluralledges thereon defining slots to hold wafers of a predetermined size,said ledges on said sidewalls having at least one surface thereof slopedto be at least 5 degrees out of parallel with the plane of said slots;said carrier further comprising an elastic element on an inner surfacethereof, said elastic element holding wafers of said predetermined sizesecure against free movement.

According to the present invention there is provided: a method oftransporting integrated circuit wafers during fabrication, comprisingthe steps of: carrying said wafers under vacuum in a vacuum-tightcarrier comprising a body including sidewalls and also a cover closeableto make a vacuum-tight seal with said body, said sidewalls each havingplural ledges thereon defining slots to hold wafers of a predeterminedsize, said ledges on said sidewalls having at least one surface thereofsloped to be at least 5 degrees out of parallel with the plane of saidslots.

According to the present invention there is provided: a method oftransporting integrated circuit wafers during fabrication comprising thesteps of: carrying said wafers under vacuum in a vacuum-tight carriercomprising a body including sidewalls and also a cover closeable to makea vacuum-tight seal with said body, said sidewalls each having pluralledges thereon defining slots to hold wafers of a predetermined size,said ledges on said sidewalls having at least one surface thereof slopedto be at least 5 degrees out of parallel with the plane of said slots:said carrier further comprising an elastic element on an inner surfacethereof; said elastic element holding wafers of said predetermined sizesecure against free movement.

According to the present invention there is provided: a method offabricating integrated circuits, comprising the steps of: transportingintegrated circuit wafers during fabrication, comprising the steps of:carrying said wafers under vacuum in a vacuum-tight carrier comprising abody including sidewalls and also a cover closeable to make avacuum-tight seal with said body; said sidewalls each having pluralledges thereon defining slots to hold wafers of a predetermined size,said ledges on said sidewalls having at least one surface thereof slopedto be at least 5 degrees out of parallel with the plane of said slots;said carrier further comprising an elastic element on an inner surfacethereof, said elastic element holding wafers of said predetermined sizesecure against free movement.

According to the present invention there is provided: a method forfabricating integrated circuits, comprising the steps of: providing aplurality of wafers in a wafer carrier having a cover vacuum sealable toa body, said body including slots for holding wafers; placing said wafercarrier into a vacuum sealable load lock attached to a process module;pumping down said load lock to a pressure less than 10 to the -4 Torr,so that said vacuum seal between said carrier body and carrier coverreleases; removing said carrier body from said cover, while said coverremains in said lock, so that wafers inside said carrier body are neverexposed in line-of-sight to any substantial portion of the interior ofsaid load lock; extending a transfer arm into said wafer carrier body,to remove a selected one of said wafers therefrom; transferring wafersin a desired sequence from said wafer carrier under vacuum to one ormore selected process stations and back until a desired sequence ofprocessing operations has been completed; and then closing said wafercarrier and raising the pressure of said load lock to approximatelyatmospheric, so that said wafers remain in vacuum inside said wafercarrier while said wafer carrier is held closed by differentialpressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to theaccompanying drawings, wherein:

FIG. 1 shows a sample embodiment of a vacuum load lock according to thepresent invention, with a wafer carrier according to the presentinvention shown therein in the process of loading and unloading;

FIGS. 1a through 1e show another sample embodiment, wherein the wafercarrier 10 prime is configured so that, instead of having an openablesealed door 14, it has a liftable sealed cover 14 prime, which is joinedto the body of the wafer carrier by a vacuum seal 13 prime;

FIG. 2 shows a graph of the time required to fall through air at variouspressures for various particulate sizes;

FIG. 3 shows a sample wafer transfer structure, in a processing station,wherein the wafer is placed onto three pins by the transfer arm 28reaching through the port 30 from the adjacent load lock 12;

FIG. 4 shows a closer view of a sample embodiment of the wafer carrier10, docked onto the platform 18 inside the load lock 12 to providemechanical registration of the position of the wafers;

FIG. 5 shows a plan view of a sample processing module, containing fourprocess stations and two wafer transfer stages, and a load lock adjacentto each of the wafer transfer stages.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The making and use of the presently preferred embodiments will now bediscussed in great detail. However, it should be appreciated that thepresent invention provides widely applicable inventive concepts, whichcan be embodied in a tremendous variety of specific contexts; thespecific embodiments discussed are merely illustrative of specific waysto make and use the invention, and do not delimit the scope of theinvention.

FIG. 1 shows a sample embodiment of the invention. This embodiment showsa wafer carrier 10 inside a vacuum load lock chamber 12. The wafercarrier 10 is also shown, in slightly greater detail in FIG. 4.

The carrier 10 is shown with its door 14 standing open. The door 14preferably has a vacuum seal 13 where it mates with the body of thecarrier 10, so that the wafer carrier can be carried around underatmospheric pressure for at least several days (preferably at leastseveral tens of days) without enough leakage to raise the internalpressure above 10⁻⁵ Torr.

The wafer carrier 10 is adapted to dock with a platform 18 (which isonly partially visible in FIG. 1, but is shown in more detail in FIG.4), so that, when a technician places a wafer carrier 10 inside the loadlock 12, the position of the carrier 10 will be accurately known. In thepresently preferred embodiment, the wafer carrier 10 has ears 16 whichengage vertical slots 17 fixed to the position registration platform 18,so that the technician can slide the carrier into these slots until itrests on the platform 18, and thereby assure that the position of thecarrier 10 is definitely known. In the presently preferred embodiment,the platform 18 includes two tapered pins 21 (one conical and onewedge-shaped) positioned to engage tapered holes 23 in the underside ofthe wafer carrier 10, but a wide variety of other arrangements could beused to assure mechanical registration, as will be obvious to anyordinarily skilled mechanical engineer.

The carrier 10 preferably has a safety catch 15 on it which secures thedoor 14 from falling open. However, under normal conditions oftransport, this safety catch is not needed, since atmospheric pressureholds the door 14 shut against the internal vacuum of the carrier. Whenthe carrier 10 is placed inside the load lock 12, a fixed finger 19 willpush against the safety catch 15 to release it, so that the door 14 canbe opened.

When the carrier 10 is docked with the platform 18, the door 14 willalso be engaged with the door opening shaft 24. Preferably the door 14has a shallow groove in its underside, which mates with a finger and arm25 on the top of the door opening shaft 24. Thus, after the load lockhas been pumped down so that differential pressure no longer holds thedoor 14 closed, the door can be opened by door opening shaft 24.

After the technician has placed the wafer carrier 10 in the vacuum loadlock 12 and closed the load lock lid 20, a high pressure purge (with drynitrogen or other clean gas) is preferably applied through manifold 22inside load lock lid 20. This high pressure purge provides verticalflow, to tend to transport particles downward, and also helps to blowoff some of the large particles which will have collected on the wafercarrier 10 during its exposure to atmospheric conditions. After thisinitial purge stage (e.g. for 30 seconds or more), the chamber is thenslowly pumped down to 10⁻⁴ Torr or less. This pump down stage ispreferably relatively slow, in order not to stir up random particulates.That is, while low pressures do permit particles to fall from the air,those particles will still be available on the bottom of the chamber,and must not be stirred up if this can be avoided.

In order to make sure that the airborne particulates have actuallyfallen out of the chamber air, the interior of the vacuum load lock willthen preferably be allowed to stay at 10⁻⁴ or 10⁻⁵ Torr for a fewseconds, to make sure that all of the particles which are able to fallout of the air will do so.

It may also be advantageous, as an optional modified embodiment of theinvention, to use a sloped bottom and/or polished sidewalls for the loadlock, to reduce the population of particulates sticking to the sidewallsand bottom which can be sent flying by mechanical vibration. The presentinvention greatly reduces the problems of airborne particulates, whichhas always been the dominant type of particulate transport, so that theproblem of ballistically transported particulates can now be usefullyaddressed. A related optional modification is the use of an in-situvacuum particle counter in the upper chamber, so that any increase inparticle population in the critical volume can be detected. Such anin-situ particle counter can be built using a resonant circuit tomeasure charge transfer in a high-voltage vacuum-gap capacitor, or (forparticles sufficiently large) by using a laser-driven optical cavitywith a multiply-folded optical path, or by other means.

Optionally, this particulate sensor (or a second particulate sensorwhich is better adapted to sensing particulates at higher pressures) canbe used to control the nitrogen shower prior to initial pumpdown. Thatis, instead of doing the nitrogen shower simply for a fixed duration, itmay be protracted if the particulate monitor shows that the box was inan unusually dirty environment. It may even be desirable to pump theload lock down to a soft vacuum (using the roughing pump) and then bleedgas through the nitrogen shower ports, to create a downward flow. It mayalso be desirable to cycle the load lock from a soft vacuum (e.g. 100milliTorr or so) up to atmospheric again, by initiating another nitrogenshower cycle, if the particulate monitor indicates that that particulatelevel is still excessive at the time the load lock has reached a givensoft vacuum pressure.

Note that vacuum gauges 62 are preferably connected to the interior ofthe load lock chamber. Preferably the sensors 62 include a high-pressuregauge (such as a thermocouple), a low pressure gauge (such as anionization gauge), and a differential sensor which accurately senseswhen the load lock interior pressure has been equalized with theatmosphere. Thus, the door of a carrier 10 is not opened until thesegauges indicate that a good vacuum has been achieved inside the loadlock.

After a roughing pump (not shown) has brought the chamber down to a softvacuum, the gate valve 39 can be opened to connect the turbomolecularpump 38 to the interior of the load lock, and the turbomolecular pump 38can then be operated to bring the pressure down to 10⁻⁵ Torr or less.

At this point, the pressures inside the wafer carrier 10 and the vacuumload lock 12 are more or less equalized, and the door 14 can beactivated by operating motor 26, which is connected to door openingshaft 24 through vacuum feedthrough 25.

Preferably two sensor switches are also included inside vacuum load lock12, to ascertain when door 14 is in its fully opened position, and whendoor 14 is fully shut. Thus, after the load lock 12 has been pumped downand allowed to sit for a few seconds, door openings shaft 24 is rotatedto open the door 14, until the sensor detects that the door is fullyopen. During this time, the transfer arm 28 is preferably kept in itshome position at an elevation below the bottom of the door, so that thedoor 14 has clearance to open. After the sensor detects that the door 14is fully open, the transfer arm can begin to operate.

The transfer arm 28 preferably has two degrees of freedom. One directionof motion permits the transfer arm 28 to reach into carrier 10 orthrough port 30 into the adjacent processing chamber. The other degreeof freedom corresponds to vertical motion of the transfer arm 28, whichpermits selection of which wafer inside the carrier 10 is to be removed,or which slot a wafer is to be placed into.

In the presently preferred embodiment, an elevator drive motor 32 isused to control the elevation of the transfer arm 28, and arm drivemotor 34 controls the extension and retraction of the transfer arm 28.Note that both of these motors, in the presently preferred embodiment,do not require vacuum feedthrough, but are housed inside the exhaustmanifold 36 which leads from the load lock 12 to the vacuum pump 38,which may be, for example, a turbomolecular pump. Moreover, the exhaustmanifold 36 does not open directly into the load lock chamber 12, butinstead has apertures 40 around its top. That is, the exhaust manifold36 is preferably configured so that there is not any line of sight pathfrom the drive motors 32 or 34 or from the pump 38 into the load lockchamber. This helps to reduce ballistic transport of particulates fromthese moving elements into the load lock chamber.

The elevator drive motor 32 is preferably connected to drive asub-platform 42 up and down, and the arm drive motor 34 is preferablymounted on this platform 42.

In the presently preferred embodiment, a linkage is used inside therotatable transfer arm support 44, to permit the transfer arm 28 to movevery compactly. The transfer arm support 44 is preferably connected to arotating rod which is driven by the arm drive motor 34, but the armsupport 44 is preferably mounted on a tubular support 46 which does notrotate. An internal chain and sprocket linkage is preferably used sothat the joint between arm support 44 and transfer arm 28 moves withtwice the angular velocity of the joint between arm support 44 andtubular support 46. (Of course, many other mechanical linkages couldalternatively be used to accomplish this.) This means that, when the armsupport 44 is in its home position, a supported wafer 48 will beapproximately above the tubular support 46, but when the arm support 44is rotated 90 degrees with respect to the tubular support 46, thetransfer arm 28 will have been rotated 180 degrees with respect to thearm support 44, so the transfer arm can either extend straight into thewafer carrier 10 or else straight through the port 30 into the adjacentprocessing chamber. This linkage is described in greater detail in U.S.patent application Ser. No. 664,448, filed 10/24/84 (TI-10841), which ishereby incorporated by reference.

The transfer arm 28 preferably is a thin piece of spring steel, e.g.0.030 inch thick. The transfer arm has 3 pins 50 on it to support thewafer. Each pin 50 preferably includes a small cone 52 on a smallshoulder 54. The cone 52 and shoulder 54 are preferably made of amaterial which is soft enough to not scratch silicon. In the presentlypreferred embodiment, these portions (which are the only portions oftransfer arm 28 which will actually touch the wafers being transported)are preferably made of a high-temperature plastic (i.e. a plastic with arelatively low propensity to outgas under vacuum) such as Ardel (athermoplastic phenyl acrylate, made by Union Carbide) or Delrin. Notethat the use of cones 52 at the center of the locating pins 50 permitsvery slight misalignments of the wafer to the transfer arm 28 to becorrected: in other words the system of wafer transport according to thepresent invention is a stable mechanical system, wherein smallmisalignments during successive operations will not accumulate, but willbe damped out.

Note that, in the positioning of the wafer 48 as shown, one of the threepins 50 rests against the flat portion 56 of the wafer's circumference.This means that, in this embodiment, the three pins 50 on the transferarm 28 do not define a circle of the same diameter as the diameter ofthe wafers 48 to be handled.

To assure that the wafer flats 56 do not interfere with accuratehandling of the wafers, the box 10 preferably has a flat surface on itsinterior back side which the flats 56 of the wafers 48 will restagainst. A spring compression element on the inside surface of the door14 pushes each wafer against this flat surface when the door 14 isclosed, so that the wafers do not rattle around in transit. This alsoassures that, when the door 14 is opened, the location of the flat 56 oneach wafer 48 is accurately known.

Thus, after the box 10 is in the chamber 12 with its door 14 open,elevator drive motor 32 is operated to bring the transfer arm 28 to justbelow the height of the first wafer which it is desired to remove, andarm drive motor 34 is then operated to extend the transfer arm 28 intothe interior of the box 10. By operating the elevator drive motor 32briefly, the transfer arm 28 is then raised, in this position, until thethree pins 50 around its circumference lift the desired wafer off of theledges 60 on which it has been resting inside the carrier box 10.

Note that the ledges 60 preferably have tapered surfaces rather thanflat surfaces, so that contact between the ledges 60 and the wafer 48resting on them is a line contact rather than an area contact, and islimited to the edge of the wafer. That is, in prior art wafer carriersarea contact may be made over a substantial area, of many squaremillimeters, but the line contact used in the present invention makescontact only over a much smaller area, typically of a few squaremillimeters or less. An alternative definition of the line contact usedin this embodiment of the invention is that the wafer support contactsthe surface of the wafer only at points which are less than onemillimeter from its edge.

Thus, by raising the transfer arm 28, the desired wafer 48 will bepicked up, and will be resting on the cones 52 or shoulders 54 of thethree pins 50 on the transfer arm 28.

In the presently preferred embodiment, the ledges 60 have acenter-to-center spacing of 0.187 inches inside the box. This centerspacing, less the thickness of the wafers, must allow clearance enoughfor the height of the transfer arm 28 plus the pins 50, but need not bemuch more. For example, in the presently preferred embodiment, thetransfer arm is about 0.080 inch thick, including the height of thecones 52 on the transfer pins 50. The wafers themselves will be about0.021 inch thick (for the presently preferred embodiment wherein 4 inchwafers are used) so that about 0.085 inch clearance is available. Ofcourse, larger diameter wafers will have greater thicknesses, but thepresent invention is eminently suited to such larger diameter wafers,since the size of the box 10 and the center spacing of the ledges 16inside the box 10 can simply be scaled appropriately.

Thus, after the transfer arm 28 has picked up a desired wafer 48, thearm drive motor 34 is operated to bring the transfer arm 28 to the homeposition.

The elevator drive motor 32 is then operated to bring the transfer arm28 to a height where it can reach through the port 30.

Port 30 is preferably covered by an isolation gate 31 unlike the gate 31shown in FIG. 3: the gate 31 preferably seals the port 30 without makingsliding contact. (Again, the absence of sliding contact is advantageousto reduce internally generated particulates.)

In the present embodiment, the isolation gate 31 over port 30 ispreferably operated by an air cylinder, but a stepper motor may be usedinstead. Thus, a total of four motors are used: two which use vacuumfeedthroughs, and two which are preferably contained inside the exhaustmanifold 36.

The arm drive motor is now operated again, to extend the transfer arm 28through port 30 into the adjacent processing chamber.

The adjacent processing chamber may be any one of many different kindsof processing stations. For example, this station may be an implanter, aplasma etch, or a deposition station.

In the presently preferred embodiment, the transfer arm reaching throughthe port 30 will place the wafer 48 on three pins 50, as shown in FIG.3, like those used in the transfer arm itself. (Note that the port 30preferably has enough vertical height to permit some vertical travelwhile the arm 28 is extended through port 30, so that arm 28 can movevertically to lift a wafer from or deposit a wafer onto pins 50 insidethe processing chamber.)

Alternatively, the processing chamber may include a fixture havingspaced sloped ledges like the ledges 16 inside the transfer box, or mayhave other mechanical arrangements to receive the wafer. However, in anycase, the arrangement used to receive the transferred wafer must haveclearance on the underside of the wafer (at least at the time oftransfer), so that the transfer arm 28 can reach in on the underside ofthe wafer to emplace or remove it. If pins 50 are used to receive thetransferred wafer, it may be desirable to provide a bellows motion or avacuum feedthrough in order to provide vertical motion of the wafersupport pins inside the processing chamber. Thus, for example, where theprocessing chamber is a plasma etch or RIE (reactive ion etch) station,a feedthrough may be provided to position the wafer 48 onto a susceptorafter the transfer arm 28 has been withdrawn out of the way of thewafer.

Of course, the processing chamber may be an engineering inspectionstation. A vacuum-isolated microscope objective lens will permitinspection of wafers in vacuum and (using an appropriately foldedoptical path) in a face-down position. This means that heavy use ofengineer inspection can be made where appropriate, without the loss ofengineer time and clean-room quality which can be caused by heavytraffic through a clean-room.

In any case, the transfer arm 28 is preferably withdrawn, and theisolation gate over port 30 closed, while processing proceeds. Afterprocessing is finished, the isolation gate over port 30 is opened again,the arm 28 is extended again, the elevator drive motor 32 is operatedbriefly so that the arm 28 picks up the wafer 48, and the arm drivemotor 34 is again operated to bring the transfer arm 28 back into thehome position. The elevator drive motor 32 is then operated to bring thetransfer arm 28 to the correct height to align the wafer 48 with thedesired slot inside the wafer carrier. The arm drive motor 34 is thenoperated to extend the transfer arm 28 into the wafer carrier 10, sothat the wafer 48 which has just been processed is sitting above itspair of ledges 60. The elevator drive motor 32 is then briefly operatedto lower the transfer arm 28, so that the wafer is resting on its ownledges 60, and the arm drive motor 34 is then operated to retract thetransfer arm 28 to home position. The sequence of steps described aboveis then repeated, and the transfer arm 28 selects another wafer forprocessing.

Note that, with the mechanical linkage of the transfer arm 28 and armsupport 44 described above, the wafers being transferred will move inexactly a straight line if the center to center lengths of transfer arm28 and arm support 34 are equal. This is advantageous because it meansthat the side of the wafer being transferred will not bump or scrapeagainst the sides of the box 10 when the wafer is being pulled out of orpushed into the box. That is, the clearances of the wafer carrier boxcan be relatively small (which helps to reduce particulate generation byrattling of the wafers during transport in the carrier) without riskingparticulate generation due to abrasion of the wafers against the metalbox sides.

Processing continues in this fashion, wafer by wafer, until all thewafers inside the carrier 10 (or at least as many of them as desired)have been processed. At that point the transfer arm 28 is returned emptyto its home position and lowered below the lower edge of the door 14,and the isolation gate over port 30 is closed. The door opening shaft 24is now rotated to close door 14, and provide initial contact for thevacuum seals between door 14 and the flat front surface of carrier 10,so that the carrier is ready to be sealed (by pressure differential) asthe pressure inside the load lock is increased. The load lock 12 can nowbe pressurized again. When the differential sensor of the vacuum gauge62 determines that the pressure has come up to atmospheric, the loadlock lid 20 can be opened and the wafer carrier 10 (which is now sealedby differential pressure) can be manually removed. In the preferredembodiment, a folding handle 11 is provided on the top side of thecarrier, to assist in this manual removal without substantiallyincreasing the volume required for the carrier inside the load lock.

After the carrier has been removed, it can be carried around or storedas desired. The seals 13 will maintain a high vacuum in the carriermeanwhile, so that particulate transport to the wafer surfaces (and alsoadsorption of vapor-phase contaminants) is minimized.

Note that the wafer carrier also includes elastic elements 27 mounted inits door. These elastic elements exert light pressure against the wafers48 when the door 14 is closed, and thus restrain them from rattlingaround and generating particulates. The elastic element 27 is configuredas a set of springs in the embodiment shown, but other mechanicalstructures (e.g. a protruding bead of an elastic polymer) couldalternatively be used to configure this. Where the wafers used haveflats, a flat contact surface 29 is preferably provided on the innerback surface of the wafer carrier box 10 for the slice flats to bepressed against.

Note also that the ledges 60 on the sidewalls of the carrier box 10 aretapered. This helps to assure that contact with the supported surface ofthe wafer is made over a line only, rather than over any substantialarea. This reduces wafer damage and particulate generation duringtransport. This also assists in damping out the accumulation ofpositioning errors, as discussed.

The load lock lid 20 preferably has a window in it, to permit operatorinspection of any possible mechanical jams.

An advantage of the present invention is that, in the case of manypossible mechanical malfunctions, the door of the wafer carrier 10 canbe closed before attempts are made to correct the problem. For example,if somehow the transfer arm 28 picks up a wafer so that the wafer is notsitting properly on all three of the pins 50, the door drive motor 26can be operated to close the door 14 before any attempts are made tocorrect the problem. Similarly, port 30 can be closed if the transferarm 28 can be retracted into home position. It may be possible tocorrect some such mechanical misalignment problems simply by deviatingfrom the normal control sequence. For example, the position of a wafer48 on transfer arm 28 may in some cases be adjusted by partiallyextending the transfer arm 28, so that the edge of wafer 48 just touchesthe outside of door 14, or of the isolation gate over port 30. If thisdoes not work, the load lock 12 can be brought back up to atmosphericpressure (with the door 14 of wafer carrier 10 closed) and the load locklid 20 opened so that the problem can be manually corrected.

Note that all of the operations described above can be very easilycontrolled. That is, no servos or complex negative feedback mechanismsare needed. All four of the motors described are simple stepper motors,so that multiple stations according to the present invention can becontrolled by a single microcomputer. The mechanical stability of thesystem as a whole--i.e. the inherent correction of minor positioningerrors provided by the tapered pins of the wafer supports, by the slopeof the wafer support ledges in the wafer carrier, and by the flat on thebackwall of the wafer carrier--helps to prevent accumulation of minorerrors, and facilitates easy control.

This advantage of simple control is achieved in part because goodcontrol of mechanical registration is achieved. As noted, the docking ofthe carrier 10 with platform 18 provides one element of mechanicalregistration, since the location of the platform 18 with respect to thetransfer arm 28 can be accurately and permanently calibrated. Similarly,the wafer carriers 10 do not need to be controlled on each dimension,but merely need to be controlled so that the location and orientation ofthe support shelves 60 are accurately known with respect to the bottom(or other portion) of the box which mates with support platform 18. Asdescribed above, this is preferably accomplished by having channelswhich the wafer carrier slides into until it rests on the platform 18,but many other mechanical arrangements could be used instead.

Similarly, mechanical registration must be achieved between the homeposition of the transfer arm 28 and the support pins 50 (or othersupport configuration) which the wafer will be docked to inside theprocessing chamber. However, this mechanical registration should be asimple one-time setup calibration.

Note that angular positioning will be preserved by the box itself: aswas noted, whenever the door 14 is closed, spring elements inside itwill press the wafers 48 against the flat on the interior back surfaceof the box.

Optionally, the wafer carrier 10 could be provided with a quick-connectvacuum fitting, to permit separate pumpdown on the carriers 10. However,in the presently preferred embodiment this is omitted, since it is notnecessary and since it simply provides another source of possibleunreliability.

Note that the load lock mechanism described need not be used solely withvacuum-tight wafer carriers, although that is the most preferredembodiment. This load lock can also be used with wafer carriers whichcarry atmospheric pressure inside. Although this is not the mostpreferred embodiment, it still carries substantial advantages, as isdiscussed above, over prior art load lock operations.

It should be noted that a wafer carrier as described can be made indifferent sizes, to carry any desired number of wafers. Moreover, awafer carrier according to the present invention can be used to carry orstore any desired number of wafers, up to its maximum. This providesadditional flexibility in scheduling and process equipment logistics.

FIG. 5 shows a sample further alternative embodiment wherein two loadlocks, each containing a wafer carrier 10, are both connected to aprocess module 102 which contains four process stations 104. When thetransfer arm 28 reaches through the port 30 from a load lock 12 into theprocess module 102, it places its wafer onto one of two wafer stages106. These wafer stages 106, as discussed above, can be three pinsupports or two ledge supports, or may have other mechanicalconfigurations that would be obvious to those skilled in the art, aslong as there is space underneath the supported wafer for the transferarm 28 to lower free of the wafer and retract after it has placed thewafer on the supports. (It is preferable, however, that the wafersupport used be such as to make line contact, rather than contact overany substantial area, to the under surface of the wafer.)

Another transfer arm assembly 106 is provided inside the process module.This transfer arm assembly is generally similar to the transfer armassembly 28, 44 and 46 used inside the load lock, but there are somedifferences. First, the transfer arm 28 used inside the load lock onlyneeds to move wafers in a straight line. By contrast, the transfer armassembly 106 must also be able to move radially, to select any one ofthe process modules 104. Thus, an additional degree of freedom isneeded. Second, the reach of the transfer arm assembly 106 need not bethe same as the transfer arm assemblies (28, 44, 46) used inside theload lock, and in fact the reach of transfer arm 106 is preferablylarger, to permit adequate spacing of the process stations 104. Third,the arm assembly 106 does not need as much travel in elevation as thetransfer arms 28 used in the load locks. Fourth, in the configurationshown, the transfer arm 128 will not have one of its three pins 50resting on a wafer flat, so that the diameter of the circle defined bypins 50 is not the same for arms 28 and 128, even though they arehandling wafers of the same diameter.

The transfer arm assembly 106 is preferably essentially the same as thetransfer arm assembly (28, 44, 46) used in the load lock, with thesedifferences. By making the tubular support 46 rotatable and providing athird motor to drive this rotation, a third degree of freedom for thetransfer arm is provided. Similarly, the dimensions of the transfer armcan simply be scaled as desired. Thus, transfer arm assembly 106preferably includes a transfer arm 128 rotatably mounted on a transferarm support 144. The transfer arm support 144 is pivotably mounted to atubular support 146 (not shown), and an internal shaft, fixed to thetransfer arm support 144, extends down through the tubular support 146.An internal chain drive with two to one gearing translates anydifferential rotation between tubular support 146 and arm support 144into a further differential rotation (over twice as many degrees)between arm support 144 and transfer arm 128. An arm drive motor,mounted below the transport assembly 106, is connected to rotate theshaft which is fixed to arm support 144. An arm rotation motor isconnected to rotate the tubular support 146. Finally, an elevatormechanism provides vertical motion of the transfer arm assembly 106.

Note that the vertical motion required of assembly 106 is not typicallyas much as that required of the transfer arms 28 in the load locks 12,since the transfer arm 128 will typically not need to select one ofseveral vertically separated wafer positions like those in the wafercarrier 10, but will typically merely be used to pick and place wafersfrom a number of possible wafer stations which are all on the sameplane. Thus, optionally the vertical elevation of the transfer 128 couldbe controlled by an air cylinder rather than by an elevator motorassembly as discussed above.

Thus, by rotating tubular support 146 simultaneously with the armsupport 144, the transfer arm assembly 106 can be rotated without beingextended. After the arm assembly 106 has been rotated to the desiredposition, the tubular support 146 can be held fixed while the armsupport 144 is rotated, and this will cause the transfer arm 128 toextend as described above.

Thus, after transfer arm 28 from one of the load locks 12 has placed awafer to be processed on one of the wafer stages 106, the transfer armassembly 106 is rotated (if necessary), extended at a low position sothat transfer arm 128 comes underneath the wafer, elevated so thattransfer arm 128 picks up the wafer, and retracted to its home position.The assembly 106 is then rotated again, and the transfer arm 128 isextended, so that the wafer is now located above a wafer support in oneof the process stations 104, or above the other wafer stage 106. Bylowering the arm assembly 106, the wafer can now be placed on the wafersupport or wafer transfer stage, and the arm 128 can now be retracted.

The process station 104 can now be sealed off from the main processmodule 102, and separate single-wafer processing of the wafer can begin.Meanwhile, the transfer arms 128 and 28 can perform other operations.When a wafer in a module 104 has completed processing, that processstation 104 can then be pumped down to the same low pressure as theinterior of process module 102, and process station 104 can be opened.The transfer arm assembly 106 can now be operated to remove this wafer,and transfer it either to one of the wafer stages 106 or to another oneof the process modules 104.

One advantage of the present invention is that the process modules 104can all be configured to do the same operation, which will permit wafertransport-limited throughput (even for fairly slow processingoperations), if there is a sufficient number of process stations 104 inthe process module 102; or, alternatively, different operations can beused in different ones of the process stations 104.

That is, the present invention permits the use of sequential processing,which is increasingly recognized as desirable, since processingvariations caused by adsorbed contaminants or by native oxide areeliminated. For example, two of the process stations 104 can beconfigured for oxide growth, one for nitride deposition, and one forpoly deposition, to permit complete in-situ fabrication of oxynitridepoly-to-poly capacitors. Moreover, the provision of different processsteps in the different stations 104 means that many lot splits andprocess variations can be performed simply by programming theappropriate operations, without relying on technicians to correctlyidentify which wafers should go to which machines. Thus, the capabilityto have different operations proceed in different ones of the processstations 104 provides additional processing flexibility.

Note also that the overall wafer transfer sequence is completelyarbitrary, and may be selected as desired. For example, the wafers fromone wafer carrier 10 could be completely processed and returned to thatwafer carrier 10, and the load lock 12 containing the just-processedwafers could be sealed off from process module 102, so that the wafersin the other wafer carrier 10 in the other load lock 12 could beprocessed while a technician removed the carrier full of processedwafers from the other load lock 12. Alternatively, the programmabilityand random access of this arrangement could be used to shuffle andinterchange wafers between the two carriers 10 in whatever fashiondesired.

It should also be noted that this arrangement is not at all limited totwo load locks 12 nor to four process stations 104, but the arrangementdescribed can be scaled to other numbers of process stations 104 in amodule 102, or other numbers of load locks 12 attached to a module 102,or to use of more than one transfer arm assembly 106 inside a module, ifdesired.

Note that this arrangement still preserves wafer orientation. Assumingthat wafers are carried in carrier 10 with their flats toward the backof carrier 10, they will be placed on wafer stage 106 with their flatstoward the center of module 102. Transfer arm 106 will preserve thisorientation, so that, when flats are replaced in either wafer carrier10, they will have their flats toward the back of the box.

Further classes of sample embodiments of the invention, embodying thenovel concepts disclosed in the parent applications in some additionalspecific implementations, will now be described.

For example, in FIG. 5 of the parent application, it should be notedthat this system could alternatively be configured with only onetransfer arm instead of three. That is, the wafer carrier 10 could bepositioned with respect to the central transfer arm 106 so that thecentral transfer arm 106 could reach directly through the open port intothe wafer carrier to remove wafers, without the use of the two localtransfer arms 28 in load locks 12. The advantage of this approach isthat the additional mechanisms, controls, and vacuum feedthroughsrequired to operate the transfer arms 28 are eliminated. Thedisadvantage is that the vertical axis motion of the transfer armassembly 106 must be increased, since arm assembly 106 now is requirednot merely to pick up or deposit a wafer, but to be able to access thefull range of slices stacked in a wafer carrier 10. Second, the accessport 30 must be made much larger, i.e. the port 30 must have enoughvertical extent to permit the transfer arm assembly 106 to pass throughit at the height of any of the wafers in the carrier 10. A furtherdisadvantage is that the transfer arm assembly 106 must extend over alarger physical distance than would otherwise be required, which meansthat it will be more difficult to construct and operate this arm toavoid positioning errors. (If the mechanical positioning control of thissystem is considered as a control system, the error filtering providedby the temporary location of wafers on the stages 105 has beeneliminated, and moreover the longer physical extension now required ofthe transfer arm assembly 106 means that larger raw errors inpositioning will be introduced.) Moreover, the system may not be somodular and easily expandable. Thus, this class of embodiment is atpresent less preferred, but it is a viable class of embodiments of theinvention, which may conceivably in the future become more preferred,and is therefore included here for clarity and completeness.

A further class of alternative embodiments uses a different shape wafercarrier. As discussed in the parent application as filed, a variety ofwafer carrier configurations may be used. One additional wafer carrierconfiguration will now be described here in detail.

In this configuration, as shown in FIG. 1a, the wafer carrier 10 primeis configured so that, instead of having an openable sealed door 14, ithas a liftable sealed cover 14 prime, which is joined to the body of thewafer carrier by a vacuum seal 13 prime. In this sample embodiment, ahandle 11 prime is provided on the top of the cover 14 prime, fortransporting assembly and removing the cover. Latches 15 prime, mountedon a base plate 202, are provided to engage a ledge 204 on the bottom ofthe cover and therefore make sure that the cover remains attached to thebody of the carrier 10 prime, whether or not the seal 13 prime remainstight under vacuum. Thus, this added element of the plate 202 with thesafety latches 15 prime on it permits utilization of the revised wafercarrier shape 10 prime. (This revised wafer carrier shape is closelysimilar to that used by one prior art system, namely that marketed by VGSystems.) That is, the embodiments shown in FIGS. 1a through 1e containmodifications to the basic wafer carrier normally used in certain priorart systems which permit such wafer carriers to be used in vacuumprocessing systems such as that disclosed in the parent application ofthe present application.

In the plate 202, note that the latches 15 prime include bosses 206around their base which provide location to the periphery 208 of theboss 204 at the lower edge of the cover 14 prime.

In the sample embodiment, the platform 18 prime is modified to containlocating pins 21 such that one is on-axis with the generally cylindricalshape of the wafer carrier, and a second one is off-axis to providecontrol of the radial orientation of the wafer carrier.

Thus, in this embodiment, the latches 15 prime are released manually,and the sealed carrier assembly 10 prime is placed on the platform 18prime manually. The load lock lid is closed, and, after the load lockhas been pumped down so that the vacuum seal 13 prime releases, thecover 11 prime can be separated from the body the body of the carrier,so that the wafers inside the body of the carrier 10 prime can beaccessed via transfer arm 28, as described above.

It would be possible to configure an arrangement so that the cover wasraised from the body of the carrier; but more preferably, as shown inFIG. 1b, the body 210 of the wafer carrier 10 prime is initiallysupported on a stage 212 which supports the platform 18 prime. The stage212 is then lowered, by mechanical transport element 214, so that thecover 14 prime remains supported by the upper floor 216 of the load lock12 prime, while the body 210 is lowered into a lower chamber 218 of theload lock 12 prime.

In the preferred version of this embodiment, the base plate 202 andsafety catches 15 prime are only used for transporting or storing thewafer carrier outside of the load lock chamber, and are manually removedfrom the base of the carrier 10 prime before it is placed into the loadlock 12 prime. Thus, in this embodiment, the cover 14 prime of the wafercarrier 10 prime remains in place in the upper chamber 219 of the loadlock, and provides a dirt barrier between the upper chamber 219, whichis exposed to particulates when the cover 20 prime is opened, and thelower chamber 218. When the cover 14 prime is not in place, with acarrier body 210 in the lower chamber 218, the stage 212 itself willprovide a dirt barrier against the lower surface of the partial floor216. Moreover, a vacuum seal 220 is preferably provided, so that theupper chamber 219 can itself be used as the only load lock, and thelower chamber 218 kept under vacuum. This is not necessarily preferred,but it is an optional use of this embodiment. Moreover, thisconfiguration does provide improved dirt isolation, since the upperchamber 219, which is most directly exposed to dirt, has relatively fewand smooth surfaces in it, and it is therefore easier to blowparticulates out. Thus, in this example the upper chamber 219 isconnected not only to a vacuum port 36 prime, but also to a purge port22 prime. After the upper chamber 219 is sealed and rough pumped down,purging gas can be blown through the port 22 prime. For example, it maybe desirable to blow moist air or partially ionized clean gas throughthe port 22 prime to reduce electrostatic particulate clinging.

This alternative embodiment has the further advantage that the wafersthemselves do not ever see even the surfaces in the load lock which wereexposed to particulates during loading of the carrier into the lock.Thus, the wafer carrier body, and the wafers in it, not only never seedirty ambient atmosphere, they never even see surfaces which are exposedto dirty ambient atmosphere.

The effectiveness of this dirt seal between cover 14 prime and partialfloor 216 can be further enhanced by adding an additional sealingelement. For example, a vacuum O-ring can be inset into floor 216surrounding the aperture where the carrier body will fit, to sealagainst a smooth surface on the underside of the flange of the cover.Less preferably, additional O-rings could be included in the carriercovers themselves.

Moreover, this O-ring, and the improved vacuum and dirt isolation whichis provides, can be used to permit a further (alternative and optional)mode of operation. If the upper chamber is always isolated from thelower chamber by a vacuum seal--either the seal between the lower edgeof a wafer carrier cover and the partial upper floor, or the sealbetween the elevatable stage and the partial upper floor--then thepressure and cleanliness of the upper chamber are not as critical. Insome operations, where it is desired to improve throughput of theloading operation, it may be desirable not to pump down the upperchamber to the low pressures and particulate counts needed for actualwafer transfer. For example, in extreme versions of this the upperchamber could be used merely as an air shower chamber to remove grossparticulates and provide an atmosphere comparable to a normal cleanroom. In other versions, where extremely high vacuum operations weredesired to be performed (such as molcular beam epitaxy (MBE), whichtypically requires pressures of 10⁻¹⁰ Torr or less), the upper chambercould be used for rough pumpdown to 10⁻ 5 Torr or so, to provide areduced load on the ultra-high vacuum system of the lower chamber.

In this alternative embodiment of the wafer carrier, the wafersupporting ledges 60 are still used, but are now located in two sidecolumns 226, which are opposite each other, as most clearly seen in theplan view of FIG. 1c, to provide line contact support of the waferholder 224.

Note that, in this embodiment, wafer holders 224 are used, instead ofunmounted wafers 48. This variation is not particularly advantageous,but simply provides a different embodiment of the present inventionwhich is compatible with other existing processing equipment. FIG. 1eshows a detail view of how the wafer 48 is held fixedly by an expandingspring 227 in the wafer holder 224. In any case, whether bare wafers orwafer carriers are used, reduced contact area with the wafer isdesirable to prevent generation of particulates, as discussed in theparent application and above. Thus, the ledges 60 which support thesides of the wafers 48 (or wafer holders 224) are preferably tapered,for the reasons discussed in the parent application.

In the specific embodiment using wafer holders 224, the wafer holders224 have a notch 229 which engages the back support rod 228. This notchserves the purpose of assuring location of the wafer radially; in otherwords, it now serves the same function as the flat back surface of thewafer carrier 10 pressing against the flat of the wafer 48, if a barewafer is used.

In this embodiment, note that the side support columns 226 and the backsupport rod 228 are joined at the top by a top support member 211 (whichincludes a handle extension), which provides mechanical rigidity andpermits manipulation of the exposed wafer carrier body 210.

In this embodiment, the springs 27, which prevent rattling of the wafersduring transport, are now located in the side support columns 226 assprings 27 prime, rather than being located in the door 14 aspreviously. This now means that more force may be required to remove andreplace the wafers in the carrier, so it may be desirable to make thepins on the transfer arm 28 higher, to ensure that this additional forcecan be applied without the wafer slipping off the pins.

As will be appreciated by those skilled in the art, the presentinvention can be widely modified and varied, and its scope is notlimited except as specified in the allowed claims.

What is claimed is:
 1. A method for fabricating integrated circuits,comprising the steps of:providing a plurality of wafers in a vacuumsealable wafer carrier, said wafer carrier comprising a bell jar shapecover which is vacuum sealable to a body thereof, said bell jar shapecover being removable from said body in a direction which issubstantially normal to the plane of wafers supported in said body;placing said wafer carrier into a vacuum sealable load lock upperchamber having a partial floor with an aperture therein and a stagepositioned below said aperture in close proximity to said floor; pumpingdown said load lock upper chamber to a pressure less than 10 to the -4Torr; lowering said stage in a linear, vertical direction, so that saidbell jar shape cover remains supported on said partial floor in saidupper process chamber while said body including wafers is lowered intothe lower chamber; transferring wafers in a desired sequence from saidwafer carrier under vacuum to one or more selected process stationswhich are enclosed inside a connecting contiguous vacuum-tight spacewith said lower chamber until a desired sequence of processingoperations has been completed; and then raising said stage to rejoinsaid wafer carrier body with said wafer carrier bell jar shape cover andagain effect a vacuum seal therebetween; venting said upper chamber toambient; and removing said wafer carrier from said upper chamber.
 2. Themethod of claim 1, wherein said stage effects a vacuum seal between saidupper chamber and said lower chamber when said stage is subsequently inits upper position, so that said upper chamber is hermetically sealedfrom said lower chamber while said wafer carrier is removed or emplacedin said upper chamber.
 3. The method of claim 1, wherein said upperchamber has exhaust and purging ports separate from said lower chamber;andfurther comprising the initial step of, prior to lowering said stage,purging said upper chamber with clean gas flow to reduce theparticulates therein.
 4. The method of claim 1, wherein said upperchamber, with a wafer carrier emplaced therein and the lid of said upperchamber closed, has substantially only smooth surfaces exposed on theinterior thereof to said exhaust and purging ports.
 5. The method ofclaim 1, wherein said pressure in said wafer carrier is less than 10 tothe -4 Torr at the time said wafer carrier body is resealed with saidwafer carrier bell jar shape cover.
 6. The method of claim 1, whereinsaid slots in said wafer carrier are sized to hold wafer holders of apredetermined size, said wafer holders directly supporting integratedcircuit wafers.
 7. A method for fabricating integrated circuits,comprising the steps of:providing a plurality of wafers in a vacuumsealable wafer carrier, said wafer carrier comprising a bell jar shapecover which is vacuum sealable to a body thereof, said bell jar shapecover being removable from said body in a direction which issubstantially normal to the plane of wafers supported in said body;placing said wafer carrier into a vacuum sealable load lock upperchamber having a partial floor with an aperture therein and a stagepositioned below said aperture in close proximity to said floor; pumpingdown said load lock upper chamber; lowering said stage in a linear,vertical direction, so that said bell jar shape cover remains supportedon said partial floor in said upper load lock chamber while said bodyincluding wafers is lowered into the lower chamber; transferring wafersunder vacuum in a desired sequence from said wafer carrier to one ormore selected process stations until a desired sequence of processingoperations has been completed; raising said stage to rejoin said wafercarrier body with said wafer carrier bell jar shape cover and againeffect a vacuum seal therebetween; raising the pressure of said upperchamber to ambient; and removing said wafer carrier from said upperchamber.
 8. The method of claim 7, wherein said step of pumping downsaid load lock upper chamber is a step of pumping down to a pressureless than 10 to the -4 Torr.
 9. A method for fabricating integratedcircuits, comprising the steps of:providing a plurality of wafers in avacuum sealable wafer carrier, said wafer carrier comprising a bell jarshape cover which is vacuum sealable to a body thereof; placing saidwafer carrier into a vacuum sealable load lock upper chamber having apartial floor with an aperture therein and a stage positioned below saidaperture in close proximity to said floor; pumping down said load lockupper chamber to lower the pressure; lowering said stage so that saidbell jar shape cover remains in said upper process chamber while saidbody including wafers is lowered into the lower chamber; raising saidstage to rejoin said wafer carrier body with said wafer carrier bell jarshape cover; and raising the pressure of said upper chamber to ambient.